Process for producing dispersions of water-soluble vinyl polymers and stabilizer for carrying out the process

ABSTRACT

The present invention concerns a process for producing dispersions of  watsoluble vinyl polymers and a stabilizer for carrying out this process. Such water-soluble, particularly cationic vinyl polymers, are employed on a large scale as process expediters for carrying out, for instance, separating processes in water treatment or waste-water purification, respectively, in the paper, coal and ore industries, in oil production or also in the food stuff industry, among others, for floculation, coagulation, retention or dewatering. According to the present invention, water-soluble vinyl polymers are homo- or copolymerized in the presence of a dispersion stabilizer of the invention. The stabilizer consists of a graft copolymer whose backbone is formed by polyethylene oxide and its grafted branches of cationic vinyl monomers. Among others, cationic, hydrophobically modified vinyl monomers can be advantageously employed. Copolymerizations can be carried out between cationic or non-ionic hydrophobically modified vinyl polymers and cationic or non-ionic, non-hydrophobically modified vinyl polymers.

The present invention relates to a method of manufacturing water-solublevinyl polymers and to a stabiliser for carrying out this method.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Water-soluble, particularly cationic vinyl polymers are employed on alarge scale as process expediters for carrying out for instanceseparating processes in water treatment or waste water purification,respectively, in the paper, coal and ore industries, in oil productionor also in the foodstuffs industry. They serve among other things forflocculation, coagulation, retention or de-watering. Despite the usuallysmall quantities used, these water-soluble vinyl polymers often have animportance which is determining in technology.

Manufacture of these polymers according to prior art is carried out byradical homo- or copolymerisation in a homogenous or heterogeneousphase. The homogenous solution polymerisation in water has thedisadvantage that even at polymer contents of below 10% by mass,high-viscosity systems are present, which do not permit a furtherincrease in the content of the active ingredient. The low polymercontent caused by this in the final product leads to poor space-timeyields of the synthesis and to increased transport costs in transport ofthe products to the user.

Polymerisations in the heterogeneous phase, such for example as theinverse emulsion polymerisation in organic solvents as a carrier phase,give rise in part to considerably higher contents of solid matter.However they have the disadvantage that operation with solvents requiresspecial protective measures and in application of the products, all thesolvent is released to the environment. The inverse suspensionpolymerisation in hydrophobic combustible solvents as a carrier phase infact after isolation and drying of the polymers leads to pulverulentproducts; the multi-stage process however is cost intensive and requiresmuch energy.

2. Description of the Related Art

Due to the disadvantages of a polymerisation in the heterogeneous phasewith organic solvents, the manufacture of dispersions of water-solublepolymers was therefore proposed, omitting organic solvents as carrierphase. The documents CA 2 096 472 and U.S. Pat. No. 5,403,883 describethe polymerisation of a combination of water-soluble and hydrophobicvinyl monomers, if necessary in combination with an amphiphatic monomer,in the presence of a polyalkylenether or of a polyelectrolyte, which isincompatible with the polymer to be dispersed, and has molecular weightsof <5×10⁵ g/mol. The polyalklylenether or the polyeletrolyte serves inthis case as a dispersion stabiliser. Preferably,poly(diallyldimethylammonium chloride) is used. The resultant dispersedpolymer has molar masses of at least 10⁶ g/mol. A disadvantage in themethods disclosed in CA 2 096 472 and U.S. Pat. No. 5,403,883 is thatconsiderable quantities of dispersion stabilisers, even up to 80% bymass with respect to the totality of monomers used, are brought intoplay. Furthermore, during the polymerisation, viscosity maxima canoccur, so that the viscosity of the polymerising system under certaincircumstances is greater than the viscosity of the polymerised endproduct.

The document EP 0 183 466 describes the polymerisation of water-solublemonomers in aqueous solutions of inorganic salts in the presence ofpolyols with molecular weights of up to 600 g/mol and/orpolyelectrolytes which have been obtained by homopolymerisation of ionicvinyl monomers or their statistical copolymerisation, as dispersionstabilisers.

The document U.S. Pat. No. 4,380,600 describes the copolymerisation ofwater-soluble and water-insoluble vinyl monomers to form water-solublecopolymers in aqueous solutions of inorganic salts or with addition ofthe salt after termination of the reaction. There are used as dispersionstabilisers water-soluble polymers with molar masses between 300 and10000000 g/mol, which preferably contain in their structural unit anether, hydroyl or carboxyl group, for example polyethylene glycol,polyethylene oxide or polyvinyl alcohol.

A disadvantage in the methods described in EP 0 183 466 and U.S. Pat.No. 4,380,600 is in particular that the viscosity of the resultantdispersions is comparatively high. A further particular disadvantage isthat during the polymerisation viscosity maxima are passed through,which lie in the range of the viscosity during previous solutionpolymerisation, and therefore render the process difficult.

A disadvantage in all the methods here named in prior art is that theresultant dispersions coagulate after a relatively short time, andtherefore the capacity for storage is restricted.

SUMMARY OF THE INVENTION

The object of the present invention is to make available a simplesynthesis method for manufacturing dispersions of water-soluble vinylpolymers, in particular attempts being made to obtain dispersions stableover a long period with a low viscosity both of the polymerising systemand of the polymerised end product of the dispersion. It is a furtherobject of the present invention to make available a stabiliser, by meansof which dispersions of water-soluble vinyl polymers can be producedwith the named properties.

This object is achieved by the method according to the invention and thestabiliser according to the invention as per the preambles inconjunction with the characterising features of claims 1 or 27.

By means of the radical homo- or copolymerisation of water-soluble vinylpolymers in an aqueous solution of salts, to which a stabiliseraccording to the invention has been added, dispersions are producedwhich have a low viscosity both of the polymerising and of thepolymerised system, and which have outstanding long-term stability. Evenafter lengthy storage for example sediments can be re-dispersed bysimple shaking. The stabiliser according to the invention consists of agraft copolymer, whose backbone is formed from polyethylene oxide andwhose grafted branches are formed from cationic vinyl monomers.

An advantage in the method according to the invention is that incomparison to prior art a reduced quantity of stabiliser is required andat the same time the final product has a high polymer content, i.e. ahigh final yield. In this way the space-time yield of the polymerisationis extremely high. Further advantages of the method according to theinvention reside in the fact that the polymerisation proceeds even up tohigh yields with a uniform speed. By means of the high polymer contentin the final product there are furthermore caused only low transportcosts for the user with respect to the mass of the vinyl polymer to betransported.

Advantageous further developments of the method according to theinvention and of the stabiliser according to the invention will becomeapparent from the dependent claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Advantageously, graft copolymers can be used as stabilisers, whosegrafted branches consist of the monomers diallyldimethylammoniumchloride, vinyl pyridium halogenide and/or N-vinylimidazoliumhalogenide. Furthermore, graft copolymers are particularly suitable asstabilisers, when their grafted branches are formed from monomers of thegeneral formula

    R.sub.1 --C(═CH.sub.2)--CO--D--E--N.sup.+ (R.sub.2,R.sub.3,R.sub.4)X.sup.-

in which

R₁ is hydrogen or a methyl residue,

R₂ is an alkyl residue with 1 to 2 carbon atoms,

R₃ is an alkyl residue with 1 to 2 carbon atoms,

R₄ is an alkyl residue with 1-6 carbon atoms or a benzyl residue,

D is the groupings NH or O,

E is an alkylene residue or hydroxyalkylene residue with 2 to 6 carbonatoms and

X is a halogenide, acetate or methosulphate.

In particular there may be used as a stabiliser graft copolymers whosegrafted branches have a molar mass between 1000 and 3000000 g/l and/orwhose polyethylene oxide polymer backbone has a molar mass between 2000and 2000000 g/mol.

In at least one embodiment of the present invention, the radicalinitiator is added in a quantity between 10⁻³ and 2% by mass withrespect to the overall reaction mix.

In at least one embodiment of the present invention, there are used asinorganic salts for the aqueous salt solution sodium chloride, sodiumsulphate, ammonium chloride, ammonium sulphate, ammonium carbonate,sodium dihydrogen phosphate, and/or disodium hydrogen phosphate.

In at least one embodiment of the present invention, the low-molecularweight polymeric ammonium salts have a molar mass of less than 8000g/mol.

In at least one embodiment of the present invention, used as thelow-molecular ammonium salt is poly(dimethyldiallylammonium chloride).

In at least one embodiment of the present invention, the salts are usedin quantities greater than 5% by mass with respect to the overall massof the reaction mixture.

In at least one embodiment of the present invention, the salts are usedin quantity greater than 7% by mass with respect to the overall mass ofthe reaction mixture.

In at least one embodiment of the present invention, the polymerisationis carried out under protective gas.

In at least one embodiment of the present invention the polymerisationof the vinyl monomers is carried out at a temperature between 30 and 80°C.

In at least one embodiment of the present invention, the polymerisationof the vinyl monomers is carried out at a temperature between 40 and 60°C.

A particularly advantageous configuration of the polymerisation andparticularly advantageous properties of the dispersion obtained areachieved if cationic, hydrophobically modified vinyl monomers arehomo-polymerised or cationic, hydrophobically modified and/or non-ionic,hydrophobically modified vinyl monomers are copolymerised with cationicand/or non-ionic vinyl comonomers. Particularly advantageous in thisrespect is the copolymerisation of hydrophobically modified vinylpolymers with non-hydrophobically modified vinyl comonomers. In thiscase it is sufficient to use only small quantities of the cost-intensivehydrophobically modified vinyl monomers, so that, compared to thehomopolymerisation of only hydrophobically modified vinyl monomers, costadvantages are obtained.

For the copolymerisation, there are particularly suitable as non-ionic,hydrophobically modified vinyl monomers, monomers which have at leastpartly the general formula

    CH.sub.2 ═C(R.sub.1)--CO--A--R.sub.2

in which

R₁ is hydrogen or methyl residue

R₂ is an alkyl residue with 1 to 10 carbon atoms and

A is the groupings NH or O.

The cationic vinyl comonomers more advantageously have at least partlythe general formula

    R.sub.1 --C(═CH.sub.2)--CO--A--B--N.sup.+ (R.sub.2,R.sub.3,R.sub.4)X.sup.-

in which

R₁ is hydrogen or a methyl residue,

R₂ is an alkyl residue with 1 to 6 carbon atoms,

R₃ is an alkyl residue with 1 to 6 carbon atoms,

R₄ is an alkyl residue with 1-6 carbon atoms or benzyl residue,

A is the groupings NH or O,

B is an alkylene residue or hydroxyalkylene residue with 2 to 6 carbonatoms and

X is a halogenide, acetate or methosulphate.

Among these cationic vinyl comonomers there are advantageous, amongother reasons on grounds of cost, monomers in which

R₂ is a methyl or ethyl residue,

R₃ is a methyl or ethyl residue,

R₄ is a methyl or ethyl residue,

B is an alkylene residue or hydroxyalkylene residue with 2 to 4 carbonatoms and

X is a halogenide or methosulphate.

The cationic vinyl comonomers can also consist at least partly ofdiallyldimethylammonium chloride, vinylimidazolium halogenide orvinylpyridinium halogenide.

There are suitable as non-ionic vinyl comonomers, monomers which consistat least partly of N-methyl-N-vinyl acetamide and/or of monomers of thegeneral formula

    CH.sub.2 ═C(R.sub.1)--CO--N--(R.sub.2,R.sub.3)

in which

R₁ is hydrogen or a methyl residue,

R₂ is hydrogen, an alkyl residue or a hydroxyalkyl residue with 1 to 4carbon atoms and

R₃ is hydrogen, an alkyl residue or a hydroxyalkyl residue with 1 to 4carbon atoms.

The method is further simplified in that the graft copolymers of thedispersion stabiliser can be generated during polymerisation of thewater-soluble vinyl monomers, according to which, by interaction ofradicals, radical structures have been formed on the backbone chain ofthe graft copolymers. In this way a separate method step is eliminated,and the entire method is simplified. The graft copolymers can be easilyproduced in the presence of a cationic vinyl monomer by conversion ofpolyethylene oxide with potassium peroxidisulphate.

There are suitable as salts for the aqueous salt solution in particularinorganic salts and/or low-molecular polymeric ammonium salts, or theirmixtures.

In the following some embodiments given by way of example of the methodaccording to the invention and of the stabilisers according to theinvention will be described.

EXAMPLE 1 Synthesis of the Dispersion Stabiliser

A thermostatised double-jacket reactor with regulated internaltemperature, with a stirring mechanism, a back-flow cooler, temperaturesensor and gas introduction device is filled with 30 g of an 80% aqueoussolution of methylacryloyloxyethyltrimethyl ammonium chloride, 30 gpolyethylene oxide (molecular weight at will between 2000 and 2000000g/mol) and 270 g water. Then the apparatus is flushed with nitrogen foran hour with continuous stirring and thereafter heat treated to 50° C.Thereafter 50 ml of the solution are removed, cooled to roomtemperature, 4 g of potassium peroxidisulphate suspended therein bystirring, and then passed back into the reactor. Then the reactionmixture is poured on ice and freed of low molecular electrolytes byultra-filtration (membrane exclusion limit 10000 Dalton). The solvent isremoved by freeze drying. After extraction with acetone, the graftcopolymer remains. The ratio of polyether unit to cationic units lies at2.5:1.

EXAMPLE 2

In a reactor as in Example 1, 26.5 g of a 75% aqueous solution ofmethacryloyloxethyldimethylbenzyl ammonium chloride, 17.7 sodiumchloride, 1.5 g of the dispersion stabiliser from Example 1 and 68.6 gof de-ionised water are added. Then the apparatus is flushed withnitrogen for an hour with continuous stirring, and thereafter heated to50° C. Thereafter the solution of 0.271 g 2,2' azobis (2-amidinopropane)hydrochloride is added in 5 ml of water. The mixture is kept at 50° C.for a further 60 minutes with continuous stirring. The final conversioncomes to 99%, the dispersion has a viscosity of 20 mPas. The molar massof the polymer comes to 2×10⁶ g/mol.

EXAMPLE 3

With a procedure identical to Example 2, 130.4 gmethacryloyloxethyldimethylbenzyl ammonium chloride, 76 g acrylamide,159 g sodium chloride, 29 g of the stabiliser from Example 1, 794 gwater and 2.44 g of the azoinitiator are used.

The reaction is terminated after 60 minutes. The final yield is 98%, theviscosity of the resultant dispersion comes to 24 mpas.

EXAMPLE 4

With a procedure identical to Example 2, 145.1 g of the solution ofmethacryloyloxethyldimethylbenzyl ammonium chloride, 88.9 g sodiumchloride, 24.1 g polyethylene oxide (molecular weight 160 g/mol) and575.5 g water are used. After addition of 0.61 g of the azoinitiator,dissolved in 10 ml water, the homopolymerisation of the cationic monomerand the graft copolymerisation of the cationic monomer occur in parallelon the polyethylene oxide backbone chain. After 100 minutes the reactionis terminated. The final yield is 99%, the molar mass of the polymercomes to 8×10⁶ g/mol. The viscosity of the resultant dispersion is 40mPas.

EXAMPLE 5

With a procedure identical to Example 4, 171.5 gmethacryloyloxethyldimethylbenzyl ammonium chloride, solution, 80.6 gsodium chloride, 32.7 g polyethylene oxide (molecular weight 35000g/mol), 532.4 g water and 0.52 g azoinitiator are used.

Duration of the reaction 110 minutes. The final yield is 99%, the molarmass of the polymer comes to 3.2×10⁶ g/mol. The viscosity of thedispersion is 40 mPas.

EXAMPLE 6

With a procedure identical to Example 4, 128.5 gmethacryloyloxethyldimethylbenzyl ammonium chloride solution, 23.9 gacrylamide, 105.8 g sodium chloride, 27.1 g polyethylene oxide(molecular weight 100000 g/mol), 556.8 g water and 0.47 g azoinitiatorare used. After 90 minutes, the conversion is 99%, and the viscosity ofthe dispersion is 25 mpas.

What is claimed is:
 1. Method for manufacturing dispersions ofwater-soluble vinyl polymers, comprising the step of polymerizing anaqueous solution of salts, a stabiliser, water-soluble vinyl monomersand an initiator, wherein the water soluble vinyl monomers are radicallyhomo- and/or copolymerised in this salt solution, characterised in thatthe stabiliser consists of a graft copolymer, the backbone of which isformed from polyethylene oxide and the grafted branches of which areformed from cationic vinyl monomers.
 2. Method according to claim 1,characterised in that cationic hydrophobically modified vinyl monomersare homopolymerised as water-soluble vinyl monomers.
 3. Method accordingto claim 1, characterised in that cationic hydrophobically modifiedand/or non-ionic hydrophobically modified vinyl monomers arecopolymerised with cationic and/or non-ionic vinyl comonomers aswater-soluble vinyl monomers.
 4. Method according to claim 1,characterised in that the graft copolymers are generated by conversionof polyethylene oxide with potassium peroxidisulphate in the presence ofa cationic vinyl monomer.
 5. Method according to claim 1, characterisedin that a stabiliser is used whose grafted branches are formed from themonomers diallyldimethylammonium chloride, vinylpyridiumhalogenide,N-vinylimidazolium halogenide and/or from monomers of the generalformula

    R.sub.1 --C(═CH.sub.2)--CO--D--E--N.sup.+ (R.sub.2,R.sub.3,R.sub.4)X.sup.-

in which R₁ is hydrogen or a methyl residue, R₂ is an alkyl residue with1 to 2 carbon atoms, R₃ is an alkyl residue with 1 to 2 carbon atoms, R₄is an alkyl residue with 1-6 carbon atoms or a benzyl residue, D is thegroupings NH or O, E is an alkylene residue or hydroxyalkylene residuewith 2 to 6 carbon atoms and X is a halogenide, acetate ormethosulphate.
 6. Method according to claim 1, characterised in that astabiliser is used whose grafted branches have a molar mass between 1000and 3000000 g/mol.
 7. Method according to claim 1, characterised in thata stabiliser is used whose polyethylene oxide polymer backbone has amolar mass between 2000 and 2000000 g/mol.
 8. Method according to claim1, characterised in that the stabiliser is used in quantities of 1 to10% by mass relative to the mass of the water-soluble vinyl monomers tobe polymerised.
 9. Method according to claim 1, characterised in thatthe graft copolymers are generated by graft polymerisation duringpolymerisation of the water-soluble vinyl monomers.
 10. Method accordingto claim 1, characterised in that a 2,2'-azobis-(2-amidinpropane)hydrochloride is added as a water-soluble initiator.
 11. Methodaccording to claim 1, characterised in that the radical initiator isadded in a quantity between 10⁻³ and 2% by mass with respect to theoverall reaction mix.
 12. Method according to claim 3, characterised inthat the non-ionic, hydrophobically modified vinyl monomers have atleast partly the general formula

    CH.sub.2 ═C(R.sub.1)--CO--A--R.sub.2

in which R₁ is hydrogen or a methyl residue, R₂ is an alkyl residue with1 to 10 carbon atoms and A is the groupings NH or O.
 13. Methodaccording to claim 3, characterised in that the cationic vinylcomonomers have at least partly the general formula

    R.sub.1 --C(═CH.sub.2)--CO--A--B--N.sup.+ (R.sub.2,R.sub.3,R.sub.4)X.sup.-

in which R₁ is hydrogen or a methyl residue, R₂ is an alkyl residue with1 to 6 carbon atoms, R₃ is an alkyl residue with 1 to 6 carbon atoms, R₄is an alkyl residue with 1-6 carbon atoms or benzyl residue, A is thegroupings NH or O, B is an alkylene residue or hydroxyalkylene residuewith 2 to 6 carbon atoms and X is a halogenide, acetate ormethosulphate.
 14. Method according to claim 13, characterised in thatin the general formula for the cationic vinyl comonomers,R₂ is a methylor ethyl residue, R₃ is a methyl or ethyl residue, R₄ is a methyl orethyl residue, B is an alkylene residue or hydroxyalkylene residue with2 to 4 carbon atoms and X is a halogenide or methosulphate.
 15. Methodaccording to claim 3, characterised in that at least a portion of thecationic vinyl comonomers comprises diallyldimetlhylammonoium chloride,vinylimidazolium halogenide, and/or vinylpyridinium halogenide. 16.Method according to claim 3, characterised in that at least a portion ofthe non-ionic vinyl comonomers comprises N-methyl-N-vinyl acetamideand/or of monomers of the general formula

    CH.sub.2 ═C(R.sub.1)--CO--N--(R.sub.2,R.sub.3)

in which R₁ is hydrogen or a methyl residue, R₂ is hydrogen, an alkylresidue or a hydroxyalkyl residue with 1 to 4 carbon atoms and R₃ ishydrogen, an alkyl residue or a hydroxyalkyl residue with 1 to 4 carbonatoms.
 17. Method according to claim 1, characterised in that there areused as salts for the aqueous salt solution inorganic salts and/orlow-molecular polymeric ammonium salts and/or mixtures thereof. 18.Method according to claim 17, characterised in that there are used asinorganic salts for the aqueous salt solution sodium chloride, sodiumsulphate, ammonium chloride, ammonium sulphate, ammonium carbonate,sodium dihydrogen sulphate, and/or disodium hydrogen phosphate. 19.Method according to claim 17, characterised in that the low-molecularpolymeric ammonium salts have a molar mass of less than 80000 g/mol. 20.Method according to claim 17, characterised in that there are used aslow-molecular ammonium salt poly(dimethyldiallylammonium chloride). 21.Method according to claim 17, characterised in that the salts are usedin quantities greater than 5% by mass with respect to the overall massof the reaction mixture.
 22. Method according to claim 17 characterisedin that the salts are used in quantities greater than 7% by mass withrespect to the overall mass of the reaction mixture.
 23. Methodaccording to claim 1, characterised in that the polymerisation iscarried out under protective gas.
 24. Method according to claim 1,characterised in that the polymerisation of the vinyl monomers iscarried out at a temperature between 30 and 80° C.
 25. Method accordingto claim 24, characterised in that the polymerisation of the vinylmonomers is carried out at a temperature between 40 and 60° C.
 26. Astabiliser for carrying out the method of claim 1, characterised in thatit consists of a graft copolymer, whose backbone is formed frompolyethylene oxide, and whose grafted branches are formed from cationicvinyl monomers.
 27. A stabilizer according to claim 26, characterised inthat the grafted branches are formed from the monomersdiallyldimethylamionium chloride, vinylpyridium halogenide,N-vinylimidazolium halogenide and/or of monomers of the general formula

    R.sub.1 --C(═CH.sub.2)--CO--D--E--N.sup.+ (R.sub.2,R.sub.3,R.sub.4)X.sup.-

in which R₁ is hydrogen or a methyl residue, R₂ is an alkyl residue with1 to 2 carbon atoms, R₃ is an alkyl residue with 1 to 2 carbon atoms, R₄is an alkyl residue with 1-6 carbon atoms or a benzyl residue, D is thegroupings NH or O, E is an alkylene residue or hydroxyalkylene residuewith 2 to 6 carbon atoms and X is a halogenide, acetate odermethosulphate.
 28. A stabiliser according to claim 26, characterised inthat the grafted branches have a molar mass between 1000 and 3000000g/mol.
 29. A stabiliser according to claim 26, characterised in that thepolyethylene oxide-polymer backbone has a molar mass between 2000 and2000000 g/mol.